Ceramic die press system

ABSTRACT

A method of forming sheet metal, especially titanium, utilizing resistance heating of the sheet metal part, and forming the part by use of relatively simple ceramic dies. The forming method includes closely controlled cooling of the formed part between the forming dies before removal from the dies to eliminate undesirable warping due to uncontrolled cooling.

Manchester et al.

tel [191 July 9, 1974 4] CERAMUIC Dill) PRESS Morrow 3,025,905 3/1962 Haerr 72/324 Inventors: Wimam E. Manchmmr bomita; 3,053,969 9/1962 Kerr et a1 219/117 HD Douglas B. lilngill, Hermosa Beach, both of Calif.

[73] Assignee: Northrop Corporation, Los Angeles,

Calif.

[22] Filed: Aug. 23, 11972 [21] Appl. No.: 284,422

[52] US. Cl. 2119/1153 [51] lnt. Cl B21] S/M [58] Field of Search 219/117 111), 50, 149-154; 7 72/324 [56] Relerences Cited UNITED STATES PATENTS 2,789,204 4/1957 Kilpatrick ct a1. 219/154 Primary ExaminerJ. V. Truhe Attorney, Agent, or Firm-Wi1lard M. Graham; William W. Rundle [57] ABSCT A method of forming sheet metal, especially titanium, utilizing resistance heating of the sheet metal part, and forming the part by use of relatively simple ceramic dies. The forming method includes closely controlled cooling of the formed part between the forming dies before removal from the dies to eliminate undesirable warping due to uncontrolled cooling.

3 Claims, 5 Drawing Figures Wo/wr/ c5 71MPRATURE CON THO L. 1. ER

PAIENTEDJUL 919M 3,823,303

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.l CERAMIC DIE PRESS SYSTEM The invention herein described was made in the course of Contract No. F33657-70-C-07l7 with the United States Air Force.

The present invention'relates to metal forming and, more particularly, to forming of sheet metal parts from titanium, titanium alloys and similar metals.

Currently employed apparatus for forming titanium and titanium alloy sheet metal tends to be relatively complex, elaborate, and expensive. This has been necessarily so because titanium and titanium alloys must be formed at temperatures up to ,l,500 F. Numerous methods have been devised, and proposed, for forming sheet metal at elevated temperatures, including locating a heating oven adjacent a forming press with conveying means to transfer a heated blank from the oven to the press.

Other methods, including resistance-heating the blank in place between the dies of a fonning press and removing the current flowing through the blank before forming, are also in use; as described and shown in US. Pat. No. 2,443,336.

A serious problem with forming titanium sheet metal at elevated temperatures with conventional metal formingtechniques is the tendency of the titanium to warp as it cools, necessitating considerable timeconsuming, expensive post-forming straightening operations. Since the forming presses commonly used to form titanium and like materials represent a substantial investment, it is not economically practical for'small shops to form large sheet metal parts.

To remedy these problems it is an object of our invention to provide a method and means of forming sheet metal such as titanium at elevated temperatures using relatively low cost tools.

It is another object of our invention to provide a method and means of forming titanium and other sheet metal at elevated temperatures, post-curing, and cooling the sheet metal with minimum of warping or distortion of the part.

Another object of our invention is to provide a means of .maintaining the sheet metal at forming temperature while it is being formed.

Other objects and advantages of our invention will clearly be seen by those skilled in the art in the ensuing detailed description.

We have found that warping can be eliminated by maintaining the sheet metal at a forming temperature throughout the forming operation and in some instances by close control of cooling before the formed sheet metal is removed from between the forming dies.

Briefly, our invention comprises electrical resistanceheating means attached to opposite ends or edges of the material to be formed, and a mating pair of forming dies made of electrical insulating, heat-resistant material such as ceramic, the electrical heating circuit remaining closed while the work material is being formed. Means are providedto bring the dies together with the work material between them, such means being either a conventional type press or merely the weight of the top die. In the latter case, lifting lugs or ears are provided on the upper die assembly so that a suitable device can engage the lower sides of the ears to raise and lower the upper die.

This invention will be more clearly understood by reference to the following detailed description of a preferred embodiment, and to the accompanying illustrative drawings, wherein:

FIG. l is a partial front view of the present invention illustrating the forming dies in the closed position.

FIG. 2 is a front view of the present invention illustrating the forming dies in the open position.

FIG. 3 is a perspective view of a forming press showing the forming dies in place thereon and a workpiece properly positioned and attached to current carrying bus bars.

FIG. 4 is a fragmentary enlarged view taken from FIG. 3 displaying a means for attaching the upper die to an upper platen of a forming press or the like.

FIG. 5 is a fragmentary enlarged view taken from FIG. 3 illustrating a method of attaching the bus bars to the workpiece.

Referring more specifically to the drawings, we have illustrated in FIG. I an upper die 1 and lower die 2, these dies l and 2 are fabricated from a high temperature-resistant dielectric material and having matching contoured die surfaces'4l and 5. The dies may be castable silica ceramic or machinable magnesium silicate, for example. The dies I and 2 are supported in metal frame members 6 and 7, these frame members 6 and 7 respectively provide structural reinforcing to dies 1 and 2 as well as providing a rigid structure on which holding ears 9 and 9, alignment brackets 12 and 12' and guide pins I5 and are welded. Alignment brackets 12 and 12 are provided with holes which align with guide pins 15 and I5 and assure proper mating of upper die 1 to lower die 2 during the metal forming operation. A temperature sensor 16 is imbedded into upper die 1 and is connected by electrical leads 20 to a workpiece temperature controller 17 for controlling the temperature of a workpiece 21 throughout the metal forming operation.

FIG. 2 illustrates a typical setup of the die set in an operating configuration. Lower die 2 is preferably supported on a firm base I9. Upper die I is provided with holding ears 9 and 9 welded to frame 6 by which means die I can be raised and lowered by a forklift or the like. Holding ears 9 and 9' are removably attached to lifting means 118 by means of holding clamps 25 and 25 which attach upper die ears 9 and 9 to the lifting means 18 as shown in FIG. 4. Workpiece 211 is shown in its unforrned configuration in FIG. 2 and is removably attached to electrical bus bars 26 and 26 by means of bus bar clamps 28 and 28. The base of clamps 28 and 28' are fixed to movable structures 29 and 29' respectively. These movable structures 29 and 29 allow bus bars 26 and 26' to move in relationship to each other as die I is lowered into a mating relationship with die 2.

In FIG. 3 we have illustrated dies 1 and 2 installed in a press 38,'however, it is not necessary to use a press during the metal fonning operation since upper die I may be of sufiicient weight to form the workpiece 21 without external force being applied. In certain aircraft sheet metal work we have found that only relatively low pressures are required; i.e., not greater than 50 psi. In this FIG. 3 we also show bus bars 26 and 26' fixed to movable structures 29 and 29' and they are removably attached to workpiece 21 by standard over-the-center clamps 28 and 28' as displayed in FIG. 5. Movable structures 29 and 29 are mounted on casters 31 and 31' and are free to move in relationship to each other as workpiece 21 is formed.

In normal operation lower die 2 is placed on the base 19, upper die 1 is removably attached to lifting means 18 such as a forklift by die ears 9 and 9' and clamps 25 and 25. Temperature sensor 16 is attached to the temperature controlling device 17. Upper die 1 is raised and workpiece 21 is inserted and connected to a power supply (not shown) by attaching bus bars 26 and 26 to the power supply and bus bar clamps 28 and 28' to workpiece 21. Electric current is then passed through the workpiece 21 thereby heating workpiece 21 to the required metal forming temperature. When a temperature readout device (not shown) incorporated with temperature controller 17 indicates that the proper forming temperature is reached, die 1 is slowly lowered into a mating relationship with die 2, thus fonning workpiece 21 into thedesired shape as shown in FIG. 1. After approximately five minutes the current flowing through workpiece 21 is gradually reduced as die 1 is gradually raised approximately two inches. Die 1 is held in this position until the surface temperature of die '1 is about 200 F below the forming temperature of workpiece 21. When the workpiece has cooled to about 200 F below its forming temperature, die 1 is completely opened and the formed part removed.

What is claimed is:

1. The process of forming sheet metal or the like which comprises:

a. positioning sheet metal between a pair of open dies, said dies being made of a high temperatureresistant dielectric material,

b. passing an electric current through said sheet metal while positioned between said open dies until the temperature of said sheet metal is elevated to a forming temperature,

0. gradually closing said dies to a closed position to form said sheet metal while the temperature thereof is at said forming temperature,

(1. gradually reducing the current flowing through said sheet metal and gradually opening said dies to a partially open position, and

e. stopping said current, fully opening said dies and removing the formed part.

2. Method in accordance with claim 1 wherein said dies are maintained closed for a period of time at said forming temperature.

3. Method in accordance with claim 1 wherein said dies are held in said partially open position until the temperature of said sheet metal has dropped to a desired temperature below said forming temperature before fully opening said dies. 

1. The process of forming sheet metal or the like which comprises: a. positioning sheet metal between a pair of open dies, said dies being made of a high temperature-resistant dielectric material, b. passing an electric current through said sheet metal while positioned between said open dies until the temperature of said sheet metal is elevated to a forming temperature, c. gradually closing said dies to a closed position to form said sheet metal while the temperature thereof is at said forming temperature, d. gradually reducing the current flowing through said sheet metal and gradually opening said dies to a partially open position, and e. stopping said current, fully opening said dies and removing the formed part.
 2. Method in accordance with claim 1 wherein said dies are maintained closed for a period of time at said forming temperature.
 3. Method in accordance with claim 1 wherein said dies are held in said partially open position until the temperature of said sheet metal has dropped to a desired temperature below said forming temperature before fully opening said dies. 